Computer-to-plate (CTP) technology has recently seen marked development, and a number of studies have been given to printing plate precursors for CTP. In pursuit of further streamlining the platemaking process and addressing the waste water problem, plate precursors that can be mounted on a printing press after imagewise exposure without requiring chemical development have been researched, and various techniques have been proposed to date.
A so-called on-press development system is one of the methods realizing processless platemaking, in which an exposed printing plate precursor is fixed on the plate cylinder of a printing press, and a fountain solution and ink are fed thereto while revolving the cylinder to remove non-image areas. This technique allows an exposed printing plate precursor to be mounted as is on a press and be made into a printing plate on an ordinary printing line. A lithographic printing plate precursor fit for the on-press development is required to have an image forming layer soluble in a fountain solution or an ink solvent and to have daylight handling properties for on-press development.
For example, Japanese Patent 2938397 discloses a lithographic printing plate precursor having, on a water-wettable support, a photosensitive layer made of thermoplastic hydrophobic polymer particles dispersed in a hydrophilic binder resin. According to the teachings, the precursor is exposed to an infrared laser beam to thermally bind the thermoplastic hydrophobic polymer particles to form an image, fixed to the cylinder of a printing press, and on-press developed with a fountain solution and/or ink. Designed to have sensitivity to the infrared region, the precursor is daylight safe.
JP-A-9-127683 and WO99/10186 also propose on-press platemaking after thermally binding fine thermoplastic particles.
JP-A-2001-277740 discloses an on-press developable lithographic printing plate precursor which comprises microcapsules containing a heat-reactive compound and enjoys an extended press life.
JP-A-2002-29162 alleges that a lithographic printing plate with a satisfactory press life is obtained from an on-press developable lithographic printing plate precursor of which the image forming layer comprises vinyloxy compound-containing microcapsules, a hydrophilic resin, and an acid generator.
JP-A-2002-46361 teaches that an on-press developable lithographic printing plate precursor of which the image forming layer comprises a microencapsulated epoxy compound, a hydrophilic resin, and an acid generator provides a printing plate with a satisfactory press life.
JP-A-2002-137562 teaches that an on-press developable lithographic printing plate precursor of which the image forming layer comprises a microencapsulated radical polymerizable compound, a hydrophilic resin, and an acid generator provides a printing plate with a satisfactory press life.